Optimized delivery of contents among pairs of users is one of the key issues of today's Internet and has strongly emerged as a significant business opportunity. Also, corporations are looking at the advantages of optimized delivery of contents among pairs of users as a way for employees to share files without the expense involved in maintaining a centralized server and as a way to exchange information with each other directly.
The major systems available in current practice have been analysed in terms of importance, behaviours and implications in the paper “An Analysis of Internet Content Delivery Systems”, by Stefan Saroiu, Krishna P. Gummadi, Richard J. Dunn, Steven D. Gribble, Henry M. Levy in Proceedings of the Fifth Symposium on Operating Systems Design and Implementation (OSDI 2002), Boston, Mass. (USA), Dec. 9-11, 2002.
The document points out that, besides classical World Wide Web, which has not been built for distribution of large multimedia files or documents and thus is not optimized therefor, one of most successful solutions is currently represented by file sharing applications based on peer-to-peer (p2p) approaches (such as Napster, Kazaa, Morpheus, etc.) that have been widely deployed and studied with respect to multiple aspects, including search capabilities, Digital Rights Management (DRM), privacy and others.
File sharing applications based on peer-to-peer approach allow users to devote a certain portion of their hard disk for the sharing of digital contents. Those applications include mechanisms to query the contents exposed by the totality or a subset of users and to require a transfer for contents of interest.
The white Paper “A Survey of Peer-to-Peer File Sharing Technologies”, by Stephanos Androutsellis-Theotokis, ELTRUN, Athens University of Economics and Business, Greece, 2002, outlines the elements and typical behaviours of such kind of applications, defining peer-to-peer approaches in terms of networks architectures (centralized, fully decentralized, hybrid and/or unstructured, loosely structured, structured networks). It also points out that such architectures are based on “overlay networks” which may be totally unrelated to the physical network that connects the different nodes.
The applicant notes that such a lack of interaction between the peer-to-peer architectures and the underlying communications networks precludes improvements and optimization in performance and management of data transfers through the physical network, preventing Network Providers from offering better performances, even if their own physical network supports a variety of infrastructure-based improvements.
Such a lack of real interaction with the underlying communications networks is the cause of a number of drawbacks such as:                it generates a very heavy load on the networks, due to multiple transfers of possibly huge multimedia files, which cannot be scheduled or managed in any way by a network operator because of the anarchist approach of p2p; and        it prevents users to achieve a good level of Quality of Service for their individual transfers, since it regards the underlying network as a simple transport pipe, which uses a best-effort approach and cannot employ any kind of advanced control facility.        
It should also be noticed that the transfer modalities of current peer-to-peer systems and services imply the duplication of the required digital contents from its original location onto the disk of the user requiring the transfer. Said content duplication effectively enables the receiving user to acquire permanently the exchanged content: that is at times undesirable, for example because of the existing legal regulations regarding intellectual property rights over digital contents.
It should further be noticed that in the known art users need to be connected with their computers to the network in order to engage in content sharing activities and for the whole duration of any content exchange.
Therefore, the current state of the art in content sharing among individual users in a p2p fashion suffers from at least two major drawbacks, which may be summarized as follows:                considerable network load and suboptimal transfer performance;        content duplication.        
Some optimizations have been proposed in the literature. A possible alternative to content duplication, as outlined for example in the news at www.wired.com: “Coder Finds New Way to Swap Tunes”, by Leander Kahney, Jan. 31, 2003 (as retrieved on Mar. 12, 2004 at the complete URL http://www.wired.com//news/print/0,1294,57482,00.html), can be the temporary lending and borrowing of content: in “digital” terms such issue can be achieved through the use of data streaming techniques that, however, in peer-to-peer environments has been so far largely impeded once more by the lack of sufficient network performance.
With respect to the issue of network load due to multiple transfers, patent application WO 02/089488 teaches to organize a shared repository working as a cache for transferred contents, which is located upon and works on behalf of end users connected to a given access network. However, that approach only helps when the physical end points of the peer-to-peer transfer are located within the same access or local network.
WO 03/071800 discloses an evolution of the previous method in which local caches located on the various access network hubs can receive and also redistribute content originating from users operating from remote hubs. However, such approach doesn't address the optimization of content delivery during the transfer over the transport public network between said remote access hubs, which still suffer from sub-optimal network performance.
In a different but related field, Content Delivery Networks (CDNs) are another means for the delivery of contents, which can be made efficient and optimized, in particular when used in conjunction with other mechanisms, such as QoS control and/or Traffic Engineering (e.g., Multi-Protocol Label Switching—MPLS techniques).
However, as explained for example in the above-mentioned paper “An Analysys of Internet Content Delivery Systems”, by Saroiu et al., the typical model is composed of a hierarchy of Content Providers such as web sites or streaming video sources, which partner with commercial CDN Providers to host and distribute contents to a plurality of end users or the general public.
CDNs and other mechanisms that follow hierarchical schemes are applied to one-to-many content distribution scenarios and do not address content sharing scenarios among pairs of individual users, in the fashion of peer-to-peer approach.